Urea-induced supramolecular self-assembly strategy to synthesize wrinkled porous carbon nitride nanosheets for highly-efficient visible-light photocatalytic degradation

Graphitic carbon nitride (g-C3N4) has attracted immense interest as a promising photocatalyst. To facilitate its versatile applications in many fields, new low-cost strategies to synthesize outstanding g-C3N4 need to be further developed. Although supramolecular preorganization has been considered as a promising candidate, the utilized supramolecules like melamine-cyanuric acid (MCA) are typically synthesized by expensive triazine derivatives. Herein, wrinkled porous g-C3N4 nanosheets were successfully fabricated by hydrothermal-annealing of supramolecular intermediate MCA synthesized by the cheap precursors dicyandiamide and urea. During the formation of MCA, urea could act as a facile agent to react with dicyandiamide to form melamine and cyanuric acid firstly and then assemble into MCA through hydrogen bonds. In addition, urea could serve as a porogen and decompose to generate bubbles for conducive formation of micro-size MCA self-templates and thus wrinkled porous g-C3N4 nanosheets could be obtained. The nanostructure and photocatalytic performance of g-C3N4 were optimized by modulating microstructures and physicochemical properties of MCA, which could be conveniently controlled by urea addition and hydrothermal duration. The obtained wrinkled porous g-C3N4 nanosheets exhibit highly-efficient visible-light photocatalytic degradation compared with traditional MCA-derived g-C3N4, which could remove 98.3% of the rhodamine B in 25 min. The superior photocatalytic activity is mainly attributed to the urea-induced larger specific surface area, better light harvesting ability, faster transfer and more advanced separation efficiency of the photogenerated electron-hole pairs. This research provides a new strategy for preparing high-performance porous g-C3N4 from the self-assembled supramolecule MCA synthesized by low-cost precursors.